6. How to Search for Dark Matter Underground and in Space

Summary

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How to Be Anything – Episode 6: How to Search for Dark Matter Underground and in Space

Podcast: How to Be Anything
Host: Emily McCrary (Anything & Everything Podcasts)
Original Release: August 13, 2025

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Episode Overview

This episode dives into the mysterious world of dark matter and profiles the people who dedicate their careers to searching for it—both miles underground and far out in space. Host Emily McCrary introduces physicist Dan Hooper (University of Wisconsin, director of the Wisconsin IceCube Particle Astrophysics Center) and Gavin Cox (experiment support scientist at the Sanford Underground Research Facility), who explain how we know dark matter exists, the ingenious ways we try to detect it, and what it might mean for the future of science if we finally find it. The episode blends accessible analogies, vivid storytelling, and personal accounts of unconventional scientific careers.

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Key Discussion Points & Insights

1. What is Dark Matter? The Mystery Defined

[00:47–02:25]

• Most of the universe’s matter is invisible—85% is “dark matter,” which we can't see or directly detect, but infer from its gravitational effects.

  • Dan Hooper: “We know that most of the matter in our universe is not made of atoms or really of anything else that appreciably radiates, reflects, or absorbs light. So we can't see it. But we're pretty sure...it's there because of all the ways we feel its gravity.” [01:10]

• Analogy: Dark matter is like something causing cars to swerve, even though you can’t see the object itself—its presence is only known by indirect effects.

  • Emily McCrary: “That's how we know dark matter is there, even if we haven't definitively detected it...” [02:25]

2. A Brief History of Dark Matter Science

[03:38–05:31]

• The idea is less than 100 years old, with early hints from the work of Fritz Zwicky in the 1930s and later observations by Vera Rubin and others.

  • Dan Hooper: “He noticed...the galaxies in the system we call the Coma Cluster...were all moving really fast, much faster than we could explain with the gravity of the normal matter...” [03:38]

• Over decades, scientists eliminated alternative explanations (e.g., faint stars, black holes)—suggesting dark matter is a new, unseen form of matter.

3. What Do We Actually Know About Dark Matter?

[05:33–06:19]

• We know the amount, “it’s not moving very fast,” and it’s stable, inert, and invisible.
  • Dan Hooper: “It’s some sort of stable, very inert, very invisible form of matter that isn’t moving very quick...And that’s about it.” [05:33]

4. How Do We Search for Dark Matter? Going Underground

[06:27–12:09]

• Deep Underground Detectors:
  Since the 1980s, physicists seek to directly detect dark matter—often “WIMPs” (weakly interacting massive particles)—by building massively sensitive detectors deep underground to shield from cosmic noise.

  • Detectors have gone from “something you could hold in your hand” to “tens of tons of detector mass...millions or maybe billions of times as sensitive.” Dan Hooper [06:27]

• Profile: Gavin Cox and the LZ Detector

  • Gavin Cox: “My name is Gavin Cox, and I’m an experiment support scientist at the Sanford Underground Research Facility in Leeds, South Dakota.” [07:33]
  • The LZ detector is a two-meter titanium cylinder holding nearly 10 tons of liquid xenon, isolated in a decommissioned gold mine a mile underground.
    • Gavin Cox: “We’re looking for one very specific type [of dark matter]...a WIMP...” [08:33]

• How It Works:

  • Xenon tank detects rare particle interactions: A passing WIMP might hit a xenon nucleus, producing a flash of light and a release of electrons.
    • Gavin Cox: “Depending on how much light and how many electrons are released during this interaction, we’ll be able to say whether it is or is not a dark matter interaction.” [09:27]

• The Underground Life:

  • Four days a week in the lab below ground, monitoring thousands of instruments.
    • Gavin Cox: “There’s an incredible amount of instruments inside this detector. It’s in the thousands, maybe up to 10,000.” [11:12]
  • On the quirks of the job:
    • Gavin Cox: “I remember getting on the cage for the first time six years ago and being very aware that I was standing over a mile deep hole...That was definitely scary at first...now it just turns into a commute.” [12:09]

5. Searches in Space: The Fermi Telescope and the Gamma-Ray Bump

[13:37–22:35]

• Space-Based Searches:
  While underground searches look for one kind of interaction (WIMPs colliding with xenon), space telescopes (like the Fermi Gamma Ray Space Telescope) look for other signatures—such as particles produced by the collision or decay (“annihilation”) of dark matter in space.

  • Dan Hooper: “You could detect things like gamma rays or other energetic forms of ordinary matter. If those sort of interactions are going on in our galaxy...” [15:28]

• The Axion Alternative:
  Another dark matter candidate, axions, which are light particles that interact with magnetic fields—a different focus from WIMPs.

• The Fermi Bump Discovery:

  • NASA’s Fermi Telescope (launched 2008) mapped gamma rays from the Milky Way’s center.
  • Dan Hooper and Lisa Goodenough analyzed early data, expecting to rule out dark matter models, but instead found an unexplained “bump” in the gamma-ray spectrum.
    • Dan Hooper: “There was this big bump in the spectrum, looked just like the bump you’d expect from dark matter...kind of had all the features you’d expect...” [18:25]
  • Hooper’s team’s claims endured skepticism and initial rejection—'you must be doing something wrong,' reviewers said. Only after accumulating more data and teaming with other researchers did NASA acknowledge the signal.
    • Dan Hooper: “We just couldn’t get it through peer review...We kept being told Fermi would have told us already...I thought we must have screwed something up.” [20:36]
    • With more data and better analysis, NASA ultimately issued a press release in 2014 recognizing the signal's potential significance.
    • NASA (via Emily McCrary): “A new study of gamma ray light from the center of our galaxy makes the strongest case to date that some of this emission may arise from dark matter...” [21:56]

• What’s Next?

  • The community agrees the signal exists, but debates remain: Is it truly dark matter, or an undiscovered astrophysical phenomenon?

6. What Would It Mean to Find Dark Matter?

[22:57–25:24]

• Discovery could “blow the doors off” our current understanding, leading to new branches of science—just as discovering gases led to chemistry and new elementary particles enabled quantum mechanics.
  • Dan Hooper: “When we discover new forms of matter and energy, it tends to lead to things that we weren’t anticipating...I think there’s a good reason to think that if we learn what the dark matter is, how it interacts, we would be able to learn completely new things, new branches of physics that we currently don’t have access to.” [22:57]
  • Understanding dark matter’s formation could also let us probe the conditions of the universe mere fractions of a second after the Big Bang.

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Notable Quotes & Memorable Moments

• On certainty and humility:
  • Dan Hooper: “The short answer is we don’t really know.” [01:10]
• On the size and challenge of modern experiments:
  • Dan Hooper: “Now we're talking about tens of tons of detector mass. We go, you know, miles underground and build these elaborate laboratories...they're millions or maybe billions of times as sensitive as those first dark matter detectors.” [06:27]
• On the initial fear of working a mile underground:
  • Gavin Cox: “...being very aware that I was standing over a mile deep hole and the only thing preventing me from dropping down was a couple inches of steel. That was definitely scary at first, but I've been doing it for so long that it just turns into a commute.” [12:09]
• On scientific null results:
  • Dan Hooper: “Even null results, even negative results teach us something about our universe. In this case, it teaches us what some of the things that dark matter cannot be.” [15:18]
• On the Fermi “bump” and surprising results:
  • Dan Hooper: “My first reaction wasn't dark matter. My first reaction is like, huh, what's that? ... None of those things made it go away.” [20:01]
• On the magnitude of future discovery:
  • Dan Hooper: “[Discovering dark matter] might allow us to look back farther in time than we've ever been able to look, understand the true, like, primordial conditions of our universe, infinitesimally close to the Big Bang. I, for one, am very excited to see that happen.” [25:24]

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Timeline of Important Segments

| Timestamp | Segment Description | |:----------:|-----------------------------------------------------------------------------------| | 00:47–02:25| Introduction to dark matter and its indirect detection | | 03:38–05:31| Historical context—early evidence and ruling out alternatives | | 06:27–13:37| Methods of underground detection, LZ experiment, and Gavin Cox’s day-to-day work | | 13:37–15:28| Space-based searches and what scientists look for in cosmic data | | 16:20–22:35| The Fermi Gamma-Ray “bump,” the challenge of peer review, and scientific drama | | 22:57–25:24| Implications of a discovery—how dark matter could reshape science |

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Episode Tone and Style

The episode is approachable, engaging, and laced with wonder—balancing layperson-friendly metaphors (traffic, coffee shop) with detailed accounts of scientific process and real-life anecdotes of scientists’ day jobs. Both guests and the host emphasize the humility, patience, and stubborn curiosity required to chase the invisible through career paths that few outside physics even know exist.

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Final Thought

The episode ends on a playful note, with Prof. Hooper mentioning his “physics punk rock band,” illustrating just how eclectic and varied the professional lives in science can be.

Dan Hooper: “For the purposes of this podcast, I will point out my physics punk rock band, the Spectral Distortions...We have songs that are broadly themed around physics and physics culture, including many of our things that frustrate us about physics.” [25:57]

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Recommended For:
Anyone fascinated by the mysteries of the universe, the practical realities of cutting-edge science, or the real lives of those dedicated to expanding the boundaries of human knowledge.

Transcript

[Dan Hooper]

ACAST powers the world's best podcasts. Here's a show that we recommend.

[Emily McCrary]

I'm Eden Scher.

[Gavin Cox]

And I'm Brock Ciarlelli.

[Emily McCrary]

We played best friends on the Middle.

[Gavin Cox]

And became best friends in real life.

[Emily McCrary]

We're here to rewatch the Middle with all of you.

[Gavin Cox]

Each week we'll recap an episode with behind the scenes stories, guest interviews, and what we think now, many years later.

[Emily McCrary]

There's a lot to dive into.

[Podcast Host/Announcer]

So let's get to middling.

[Dan Hooper]

ACAST helps creators launch, grow and monetize their podcasts everywhere. Acast.com.

[Emily McCrary]

We can confidently describe only 15% of what constitutes the material universe. The rest of it, the remaining 85%, is still beyond our understanding. We call it dark matter, and though we've never directly detected it, scientists are convinced it's there. So what is dark matter?

[Dan Hooper]

The short answer is we don't really know. We know that most of the matter in our universe is not made of atoms or really of anything else that appreciably radiates, reflects, or absorbs light. So we can't see it. But we're pretty sure we're virtually certain it's there because of all the ways we feel its gravity.

[Emily McCrary]

That's Dan Hooper, a professor of physics at the University of Wisconsin and the director of the Wisconsin IceCube Particle Astrophysics Center. He's also written several books, one of them about dark matter.

[Dan Hooper]

The story I like to tell is like if you wanted to know what the mass of the planet Mars was, the only way you would know that is by looking at things like its moons and see how fast they move around the place where Mars is. Essentially, you can weigh Mars by looking at the motion of its moons. And we can do the same thing with a whole galaxy. We can look at how fast stars move around our galaxy or other galaxies, and we can weigh those galaxies. When we do that, we find out that something like 85% of the total mass in these systems isn't made of stars or gas or dust or planets or anything else that interacts with light. And something else, something we call dark matter.

[Emily McCrary]

Here's my best layman's take on dark matter. Let's say you're sitting in traffic and up ahead you can see cars veering off in two directions to avoid something that's in the road. Now, you can't see what that thing is yet, but you know something is there because of the way drivers around it are behaving. You could venture a few guesses. It might be a pothole Might be a piece of rubbish, or it could be something totally bizarre you haven't imagined yet. But you could also rule out a few things. It's definitely not a redwood tree growing out of the pavement, because those things are monstrous. And you know you'd be able to see it, but you still can't say for sure what it is, at least not quite yet. That's how we know dark matter is there, even if we haven't definitively detected it, even if we can't definitively describe what it is. There are people searching for dark matter and they look deep underground and far out into space. And one of them, namely one Dan Hooper, might have found it. This is how to Be Anything, the podcast about people with unusual jobs. I'm Emily McCrary. The Theory of dark matter is relatively new, less than 100 years old.

[Dan Hooper]

But we didn't really have any evidence at all in favor of dark matter until the 1930s, when the astrophysicist Fritz Wickey, he's a Swiss American astrophysicist, he noticed that the ways in which galaxies in the system we call the Coma Cluster, those galaxies were all moving really fast, much faster than we could explain with the gravity of the normal matter in that system. So he wasn't sure what he was looking at, but he speculated maybe there was just a lot more matter in that galaxy than we could see. There was a bunch of invisible matters. I don't think anyone took it very seriously at the time. It wasn't until decades later that astronomers like Vera Rubin and others started to notice something kind of analogous to that in galaxies. Not just the Milky Way, but a bunch of other galaxies too.

[Emily McCrary]

But even then, astronomers weren't thinking, oh well, that invisible stuff must be an entirely new kind of matter altogether. They were thinking it was something we just couldn't pick up with the telescope yet, like some type of gas or burnt out stars.

[Dan Hooper]

But then by the late 70s, 1980s and into the 90s, most of these kind of mundane explanations got ruled out. We looked for things like faint stars, things like white dwarf stars and black holes and neutron stars, things that are hard to see with your telescopes and they're just not there, not in any appreciable number. So we could rule out that those sort of ordinary burnt out stars might made up the dark matter. And in their place, the leading hypothesis became the idea that there's really a new form of matter, or maybe forms, maybe it could be more than one thing. And like I said before, this stuff doesn't appreciably radiate, reflect, or absorb light. So we don't see with our telescopes, but we've increasingly become good at measuring where the stuff is through the effects of their gravity.

[Emily McCrary]

So what do we know about dark matter?

[Dan Hooper]

We know a few things. We know how much there is. We know that whatever parts or particles it's made of, those parts or particles are not moving very fast. If they were moving comparable to the speed of light or something like that even billions of years ago, the structure of our universe would look very different today. If the dark matter is slow moving and kind of made up of some sort of heavy particle or something, then we can explain why we have the number and shapes of galaxies and galaxy clusters and stuff that we observe. So we are pretty sure that whatever it is, it's some sort of stable, very inert, very invisible form of matter that isn't moving very quick. And that's about it. That's about all we can say about it at this point.

[Emily McCrary]

When did we start looking for it or trying to detect it? And how are those methods different than what we use today as far as.

[Dan Hooper]

Looking for particles of dark matter? You know, lots of these efforts go back to the 1980s or so. So one way to do this is to take a high precision, highly sensitive detector, go deep underground where cosmic radiation can't reach you, and hope that occasionally a dark matter particle will travel straight through the Earth, because they can do that, and they can get your detector, and maybe one out of a million of those particles will scatter with your detector and you'll see it. You know, we started doing this back in the late 80s. Didn't see anything, didn't see anything in the 90s, didn't see anything in the 2000s, still haven't seen anything to today. But whereas those first detectors you could, like, literally hold in your hand, they were very small and modest. Now we're talking about tens of tons of detector mass. We go, you know, miles underground and build these elaborate laboratories to host these detectors. And they're millions or maybe billions of times as sensitive as those first dark matter detectors.

[Emily McCrary]

Well, let's meet someone who does this. Spends their days underground working with a dark matter detector.

[Gavin Cox]

My name is Gavin Cox, and I'm an experiment support scientist at the Sanford Underground Research Facility in Leeds, South Dakota.

[Emily McCrary]

Gavin works with a device called the LZ Dark matter detector. LZ stands for Lux Zeppelin. The LZ is a titanium cylinder about 2 meters in diameter and 2 meters tall, containing nearly 10 tons of liquid xenon. It sits a mile underground In a decommissioned gold mine in the mountains of South Dakota, scientists run this dark matter experiment underground to get rid of something called irreducible backgrounds, which is basically just noise that gets in the way of what they're trying to identify. You might think of it this way, if you're trying to hear a friend talking to you, but you're standing on a busy city street, it's going to be a lot easier if you step inside a coffee shop to have that conversation. Instead of stepping into a Starbucks, the scientists at CERF go a mile underground. It's not a perfect environment, but it's certainly a lot easier to hear down there, so to speak.

[Gavin Cox]

So there's a lot of ideas as to what dark matter could be. We're looking for one very specific type. So that type is called a wimp, which stands for a weakly interacting massive particle. These are very small, very dense particles that are theorized to be distributed all throughout the galaxy. So that means our solar system and our planet is washing through this sea of wimps, and they just don't want to interact with anything. So the idea is that we'll have a very large detector filled with liquid xenon, and some of these wimps will come through. So scatter off the xenon nucleus and produce a signal that will be able to say, that was a WIMP interaction.

[Emily McCrary]

How do you know if you've found dark matter or not?

[Gavin Cox]

Let's get into the specifics of how our detector works. We have a giant tank filled with 9 tons of liquid xenon. So we choose xenon because it's a noble gas, and noble gases are like argon or helium. They don't really want to interact with anything. And that's nice because, again, we want a quiet experiment. And it's also the heaviest stable noble gas. So one of these WIMP particles, we're hoping that it will pass through the Earth and hit the nucleus of a xenon atom. When it does that, it'll produce two signals. The first one's a little flash of light, and. And the second one, it'll release some electrons. So depending on how much light and how many electrons are released during this interaction, we'll be able to say whether it is or is not a dark matter interaction.

[Emily McCrary]

In order for the LZ to work, that xenon has to stay really, really clean. That means air can't get in because it can produce one of those irreducible backgrounds and ruin the experiment. It also has to stay really cold, as in minus 100 degrees Celsius or roughly negative 150 Fahrenheit.

[Gavin Cox]

And then we house it in one of those double walled containers, kind of like a coffee cup or a thermos that keeps it warm or cold for a very long time. We have a great vacuum that's insulating all of the xenon and that has to be on 24 7. We can't lose vacuum for even a day.

[Emily McCrary]

Gavin spends about four days a week underground with the LZ dark matter detector. The other days he sits at a desk above ground reading data produced by the LZ and monitoring for problems.

[Gavin Cox]

There's an incredible amount of instruments inside this detector. It's in the thousands, maybe up to 10,000. This includes valves, pressures, temperatures, levels, purity. We have a way of monitoring a large amount of the detector all the time in real time. So in order to change various aspects of the detector, that's going to be through the computer. Then there's also some data analysis that I do, ensuring that we're getting quality data. If one of those photomultiplier tubes trips or turns off, it's my responsibility to know when that is and make sure that we aren't taking data during that time because it slightly changes the state of the detector and we turn it on as quickly as we can and then get back to high quality data.

[Emily McCrary]

So what's it like to spend four to five days of your week underground? Does that throw off your internal clock at all?

[Gavin Cox]

It was definitely something to get used to. I remember getting on the cage for the first time six years ago and being very aware that I was standing over a mile deep hole and the only thing preventing me from dropping down was a couple inches of steel. That was definitely scary at first, but I've been doing it for so long that it just turns into a commute.

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[Emily McCrary]

So far, we haven't detected dark matter with the lz. But while Gavin's a mile underground, other scientists are looking for dark matter in the cosmos. I know what you're thinking. Didn't we just go down there to filter out noise? Certainly there's more in space, right? Professor Dan Hooper again now looking to space.

[Dan Hooper]

There is a lot of background of energetic particles coming from space, and you have to work pretty hard to contend with that. But it turns out that those backgrounds, although they are formidable, with some clever data analysis and thoughtful astrophysics, you can try to separate the signal you're looking for from various kinds of backgrounds, at least to some degree.

[Emily McCrary]

Keep in mind that astrophysicists looking into the cosmos for dark matter aren't searching for the same thing those physicists underground are. Remember, we're not sure what dark matter is. So scientists are looking for different things. With the LZ, they're looking for WIMPs to interact with xenon. But in outer space, scientists are looking for other interactions, like maybe two particles of dark matter colliding with each other.

[Dan Hooper]

So maybe the dark matter is a little bit unstable. Maybe the age of the universe, one part in a trillion of it has decayed. And when it decays, it creates energetic stuff like maybe gamma rays or neutrinos or things like this that we could try to detect with our telescopes. We're looking for that. The other possibility is that maybe the dark matter is stable. Like, if you have a isolated particle of dark matter, it will sit around forever and do nothing. But if you get it in pairs, if you get two dark matter particles together, they might be able to destroy each other the way that, like, an electron and a positron will destroy each other if they get in proximity to each other.

[Emily McCrary]

That's an event called annihilation, in which two particles collide and visible stuff comes out. Physicists hypothesize that this might be one way we detect dark matter.

[Dan Hooper]

You could detect things like gamma rays or other energetic forms of ordinary matter. If those sort of interactions are going on in our galaxy, we also look to space to detect other kinds of particles. One kind of dark matter candidate we talk about are called axions. These are different from WIMPs. They're really, really light. They were produced in the early universe, but by a different mechanism. They don't just, like, scatter and they don't annihilate. Instead, what they do is they interact with magnetic fields in a way that we can hope to detect. We still haven't seen anything. And you might think that's entirely bad news. But. But I'll tell you, it's really informative. A lot of our best guesses about what dark matter might be made of, these experiments have told us, aren't the right guesses. So even null results, even negative results teach us something about our universe. In this case, it teaches us what some of the things that dark matter cannot be.

[Emily McCrary]

He's right. There's no official consensus that we've detected dark matter, but we might have already done it. Actually, let me rephrase that. Dan Hooper might have already done it. Tell me about what happened in 2009 and this anomaly that you detected in a data set. What was happening?

[Dan Hooper]

You know, at the time, I didn't think that much of it, but looking back, it, you know, it's this very seminal or important moment in my career, but I didn't see it coming.

[Emily McCrary]

In 2008, NASA launched the Fermi Gamma Ray Space Telescope. It's named after the Italian American physicist Enrico Fermi, who won the Nobel Prize in 1938. And then he designed and built the first nuclear reactor and was later recruited by Robert Oppenheimer to work on the Manhattan Project at Los Alamos. Kind of makes me wonder, what have I done today? Anyway, the Fermi telescope picture something with.

[Dan Hooper]

A couple of big solar panels and going around the Earth over and over again, mapping out the sky and in gamma rays. So gamma rays are just particles of light, just photons, but they have a lot of energy. In this case, they have about a giga electronovolt or so each, roughly, which is like the sort of energy you see in like, kind of particle colliders and things like this.

[Emily McCrary]

The Fermi telescope is floating around in space to do many things. One of them is attempting to find dark matter.

[Dan Hooper]

So it's, it's a lot, lot of energy in these, these photons. And when a photon like this hits the detector, the Fermi detector, it creates a track of particles so you can tell what direction that photon came in. And it has a thing called a calorimeter that measures how much energy the photon has. So you can measure the energy and direction of each of these photons and they detect tons and tons and tons of these photons. They provide a beautiful map of the whole sky. We were really excited about this because we thought you could look for the dark matter annihilation products.

[Emily McCrary]

NASA got the first rights to the initial data collected by the Fermi telescope. Then after about a year, they made all of it public.

[Dan Hooper]

Pretty soon after it went public, I and my collaborator, Lisa Goodenough, downloaded all that data. I had been thinking about how you would look for dark matter with this kind of data set for a while. So I coded up a data analysis pipeline to look for specific kinds of gamma rays coming from the center of the Milky Way. And we had every intention of writing a paper when we were done that said, here's a new limit on how much dark matter can be annihilating, and here are the new dark matter models that are ruled out by this data set. After all, that's usually what you do in the dark matter game. Usually you don't expect to find anything. There was this big bump in the spectrum, looked just like the bump you'd expect from dark matter. Furthermore, the bump got brighter as you went in closer to the galactic center. The. But you could see it well away from the galactic center, too. So it wasn't just like a point source. It was kind of a diffuse cloud of this stuff that was brightest at the galactic center, but extended out thousands of light years in every direction. So it kind of had all the features you'd expect a dark matter particle that was annihilating in our galaxy to have. Most things in nature don't make bumps. Most things in nature make kind of smooth, not obvious, kind of gradually changing spectra. This one had this bump.

[Emily McCrary]

To be clear, he and Lisa didn't start the project thinking they would find dark matter. They expected to find more information about what it isn't. But based on this initial analysis, it kind of feels like he's looking at dark matter.

[Dan Hooper]

I can literally remember, like, some of the details. My feet were on my desk, which was a bad habit. I later led to some back problems doing that all the time. But my feet were on my desk. My laptop was sitting there, my lap. I just remember looking at it like, oh, that's weird. That's funny. My first reaction wasn't dark matter. My first reaction is like, huh, what's that? You know, I kept digging into it. It kept trying to make it go away. Like, well, maybe if I did this different, maybe if I did that different. Maybe if I added this thing, maybe if I took away this thing and none of those things made it go away.

[Emily McCrary]

So they wrote a paper and gave.

[Dan Hooper]

A few talks, but we just couldn't get it through peer review. We kept being told that, no, no, no, Fermi would have told us already if this signal was there. You must be doing something wrong. Even sometimes we'd get reports from anonymous referees Saying, no, no, no. We already talked to people in Fermi and there's no signal like this. So I believed him. I thought, well, we must have screwed something up.

[Emily McCrary]

About a year later, a colleague working with the Fermi Telescope project called Professor Hoover, he looked at that paper, the one that never went anywhere, and he said, no, no, no, we see it too.

[Dan Hooper]

So Lisa and I wrote a second paper about a year after the first with twice as much data and also like considerably more sophisticated analysis techniques. And we put that out as, again, it was very controversial. People didn't like it, and it got a little bit heated at times. But this one went through peer review.

[Emily McCrary]

But still, people weren't quite buying it. So Professor Hooper assembled a bigger team with more scientists to work on an analysis of the same data.

[Dan Hooper]

We wrote a big long paper where we threw kind of every analysis technique. We'd think about it. In the end, it just looked exactly like what you'd expect from dark matter. We put that paper out, we promoted it the best we could. Finally, NASA issues a press release saying the signal was there.

[Emily McCrary]

The 2014 NASA press release begins. A new study of gamma ray light from the center of our galaxy makes the strongest case to date that some of this emission may arise from dark matter, an unknown substance making up most of the material universe.

[Dan Hooper]

Now, since then, there's been a lot of fighting back and forth. No one's fighting anymore about whether the signal is there. We all agree the signal is there, and we all pretty much agree that it looks like the signal that dark matter could at least hypothetically make. The debate is whether it's necessarily dark matter or whether a signal like that could be mimicked or kind of faked by something else.

[Emily McCrary]

The Fermi telescope keeps sending back data that expands our understanding of dark matter. Just Google Fermi telescope dark matter and check out all the amazing findings from the last 17 years. What will it mean for our understanding of the universe if, and I guess when we detect it for the first time?

[Dan Hooper]

Officially, it depends what we find out it is right, but it could be enormously significant for the history of science. So when you look back on the history of science, when completely new forms of matter were discovered, that wasn't the end of the story. That's almost always the beginning of, of the story. So when, I don't know, back in the 1700s, people are starting to figure out that there are different kinds of gases that exist. Like, oh, there's a sink called oxygen, there's a sink called nitrogen. Oh, there's a sink called hydrogen that led to chemistry, an entirely new science. And like, blew the doors off of everything we thought we knew about matter. When the first elementary particles were being discovered in the early 20th century, things like the discovery of the electron, well, you know, that coincided with the invention of quantum mechanics and the quantum nature of our universe. And frankly, nothing has been as big a deal in the history of physics, I think, than discovering of quantum mechanics and quantum physics. Later on, we discovered things like, I don't know, muons and taus and quarks and things like this. We built what we call the center model of particle physics. It just gives us a profoundly deep understanding of, of the kinds of ways in which the fields that permeate our universe work and the kinds of matter and energy that we find in our universe. The bottom line is when we look at the history of science, when we discover new forms of matter and energy, it tends to lead to things that we weren't anticipating. Past is not a guarantee that the future will be that way. But I think there's a good reason to think that if we learn what the dark matter is, how it interacts, we would be able to learn completely new things, new branches of physics that we currently don't have access to. One really straightforward thing is we're pretty confident that the dark matter, whatever it is, was formed in the first fraction of a second after the Big Bang. So if we want to know what our universe was like a millionth or a billionth or a trillionth or less of a second after the Big Bang, learning what the dark matter is and its properties is going to be one important way to do that. It might allow us to look back farther in time than we've ever been able to look, understand the true, like, primordial conditions of our universe, infinitesimally close to the Big Bang. I, for one, am very excited to see that happen.

[Emily McCrary]

How to Be Anything is written by me, Emily McCrary, Lily I. Johnson is our producer and Kaden Boffman is our editor. Visual design by Nika simovich fisher@laboud. Follow us on Instagram howtobenything and at our substack howtobenything.com you can learn more about CERF and the Fermi Telescope and Dan Hooper's work, including his podcast, why this Universe? In which he talks about the biggest ideas in physics today, including dark matter. Before you go, I'll leave you with one last thought from Professor Hooper.

[Dan Hooper]

For the purposes of this podcast, I will point out my physics punk rock band, the Spectral distortions you can find us on Spotify. We have songs that are broadly themed around physics and physics culture, including many of our things that frustrate us about physics.

[Emily McCrary]

Thanks for listening.

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